Track correction control

ABSTRACT

A mobile track laying machine arranged to move in a working direction from a newly laid corrected to a newly laid uncorrected track section corrects the position of the track at a track correction station. The track correction is controlled by a reference system which includes a reference associated with a track rail. The reference extends in a direction opposite the working direction towards the track correction station between two end points spaced from each other along the track one in the old track section and the other in the uncorrected newly laid track section, and means is provided to position the reference solely in dependence on the position of the track in the old track section.

United States Patent [1 1 Plasser et al.

Mar. 5, 1974 TRACK CORRECTION CONTROL 3,523,372 8/1970 Stewart 33/60 Primary Examiner-William D. Martin, Jr. Attorney, Agent, or Firm-Kurt Kelman [22] Filed: Jan. 19, 1970 [57] ABSTRACT [21] Appl. No.: 3,763 A mobile track laying machine arranged to move in a working direction from a newly laid corrected to a [30] F i A li ti P i it D t newly laid uncorrected track section corrects the posi- 22 [969 Austria I t 645/69 tion of the track at a track correction station. The track correction is controlled by a reference system 52 us. (:1 33/287 33/144 33/338 which ihclhdes a reference assmiated with a hack 10 4 /7 The reference extends in a direction opposite the [51] Int. Cl B6lk 9/08 working direction towards the track correction Station 5 Field of Search 44 45. R 8 between tWO end points spaced from each other along the track one in the old track section and the other in [56] References Cited the uncorrected newly laid track section, and means is provided to position the reference solely in depen- UNITED STATES PATENTS dence on the position of the track in the old track sec- 3,l44,834 8/1964 Stewart 33/60 X i 3,381,626 5/1968 Fagan et a]. 3,334,593 8/1967 Plasser et al. 104/7 R 33 Claims, 5 Drawing Figures l 7 2 l0 [2 I2 /2 l3 1 3. D T E] -I:I"-'.---H--- -:1 l I PATENTED 5 4 I N VEN TORS 2 PLASJQQ BY DSEF TH'EURER 1 TRACK CORRECTION CONTROL The present invention relates to improvements in the correction of the position of a track, and more particularly to a novel control for correction. It is particularly useful in such track laying machines or trains replacing the track in an old track section by an entirely new track.

It has been conventional to effectuate track position correction in relation to a reference system including a reference line or plane associated with one of the track rails. In these conventional reference systems, the reference has always extended from a front station in the uncorrected track section to a rear station in the previously corrected track section. The track was lifted or lined in relation to the reference whose rear end rested on the corrected track section while, seen in the working direction, the correction of the track position was effected forwardly of the rear end at a point of the reference where its position was determined by masking or like means.

While this arrangement has been found highly satisfactory in many instances, it cannot be readily used in certain automatic track working operations. For instance, it is of little use in a track renewal operation requiring the laying ofa new track in an at least relatively correct desired level and alignment. in such an operation, a rear point for fixing the'reference line in the previously corrected track section is not readily available.

It is the primary object of the present invention to provide a track correction reference system for such special situations, including a control for a sufficiently accurate positioning of a newly laid track.

The above and other objects are accomplished in accordance with this invention with a reference system which includes a reference line or plane associated with one of the track rails and which extends in a direction opposite to the working direction of the mobile track working machine towards the track correction station between two end points spaced from each other along the track one in the old track section and the other in the newly laid uncorrected track section. The position of the reference line or plane solely depends on the position of the track in the old track section.

With such an apparatus, any changes in the track level or alignment due to such track working operations as track laying may be corrected immediately during the operation itself so that the track assumes at least an approximately correct position which is good enough, at any rate, to make it possible for trains to pass thereover and which may be, if desired, further corrected to a desired degree of accuracy in a subsequent fine correction operation.

According to one preferred feature of the invention, if the reference is a reference plane, the reference plane is fixed at one of the track points in respect of a reference plane perpendicular or parallel to the plane of the track. The necessary parameters required toproduce the desired track position may be more readily determined in respect of such a fixed plane than in relation to a reference line.

The principles of the present invention may be embodied in various structures. For instance, the position of the reference may be determined solely by the position of its forward end, seen in the working direction. This may be effected by a frame guided along the associated track rail in the old track section on two running gears spaced from each other along the track. The position of such a frame corresponds to that of the old track and the reference determined by this frame position will thus depend solely on the track position in the old track section. lf the frame is of sufficient elongation, any minor unevenness in the old track section will be evened out.

In another, relatively simple embodiment, an intermediate station is arranged in the old track section in contact with the reference system, and a control for the reference positioning means is operable in dependence on the position of the intermediate station. The intermediate station may be temporary or permanent. I

The reference line or plane may be positioned by adjusti'ng the forward end of the reference and/or the intermediate station, for instance by pivoting or otherwise moving the forward end of the reference and/or the intermediate station vertically and/or laterally. Such an arrangement makes the reference system readily and rapidly adjustable.

Since the control of the superelevation of the track is also of importance, suitable and conventional means for determining and/or controlling such superelevation may be mounted either at the forward end of the reference, at an intermediate station or at the track correction station.

The reference may be constituted by a beam of electromagnetic radiation, for instance infra-red of light or and in such case, a beam masking means may be positioned at an intermediate station. The beam masking means is supported on the associated track rail and the distance thereof from the rail corresponds to the distance of the reference end from the track.

The preferred reference is a laser beam beam defining a reference line or a reference plane. In this case, it is sufficient to mount the laser beam emitter adjustably in dependence on the position of the associated track rail in the old track section, thereby to determine the position of the reference as the laser beam is projected towards the track correction station.

However, tensioned wires and like elongated mechanical elements may also be used as a reference, in which case a mechanical contact element is mounted at an intermediate'station in the old track section to determine the position of the tensioned wire when the same is in contact with the mechanical contact element, such as forked support.

The track working machine includes track working tools at the track correction station, and means at the end of the reference closer to the previously corrected track section for determining the difference between the actual and the desired position of the track at the track correction station to survey the track position at the point where it has been changed by the working tools and requires correction.

The above and other objects, advantages and features of the present invention will become more apparent in the following detailed description of certain now preferred embodiments thereof, taken in conjunction with the accompanying drawing wherein FIG. 1 is a schematic top view of a track laying or renewal machine including two trains for respectively taking up and laying track;

FIG. 2 is a schematic side view of a modified track laying and renewal machine;

FIG. 3 is a schematic side view of yet another modification of such a machine;

i of the invention.

Referring now to the drawing and first to FIG. I, the track working machine partially shown therein is an apparatus for replacing an old track by a new track, such as disclosed and claimed, for instance, in our U. S. Pat. No. 3,330,219 and No. 3,521,565. Such a machine comprises a forward train, seen in the working direction indicated by the horizontal arrow, and represented only by its last car 1 designed to receive the old ties and from which the new track rails 2 are continuously deposited at the track correction position as the train advances in the indicated working direction. The car 1 carries a means for positioning the reference line 3. If desired, this reference could be a rigid rod fixedly mounted on a carrier on the car so that the position of the car on the old track section alone determines the position of the rod in'its extension towards the track correction station, i.e. the point where the new track is laid. However, in the illustrated embodiment (see also FIG. 8), the reference is a laser beam 3 which is emitted from an emitter 7 mounted for universal adjustment on car 1.

The car 1 is supported on the old track 6 by two running gears 4 and 5 which are spaced along the track in the direction of track elongation. The emitter 7 may be adjusted so as to be parallel with the car and to project the laser beam in the direction of track elongation (or it may be fixedly mounted on the car in this position) so that the laser beam position depends solely on the position of the car on the old track and the laser beam is always parallel thereto.

To make certain that the car 1 is always in an exact relationship to the 'old track and its position corresponds accurately to that of the track, the running gears have flanged wheels whose flanges are pressed against a selected grade rail, thus making the car an accurate reference base. The illustrated means for pressing the car against the grade rail is a pressure fluid motor 8, 9 engaging the old track 6 and operating in a conventional manner.

The determination of the desired position of the newly laid track rails 2 is effected by means positioned at the rear end of the reference 3, which is constituted by a laser beam receiver 10 in the illustrated embodiment. The receiver 10 has laterally extending sensors 11 arranged for guidance along the new rails 2, such sensors consisting, for instance, of flanged rollers. A pressure fluid motor 11' is connected to the receiver for pressing the same into a selected lateral direction for engagement of a flanged roller 11 with the selected grade rail of the new track. In this manner, the entire laser beam reference system is accurately positioned in respect of the old and new tracks.

The laser beam receiver has photocells or like light or heat-sensitive elements which produce control signals upon impingement of the laser beam to operate the control 12' for the lateral movement of the conventional track lining mechanism 12 which includes rail engaging rollers laterally movable in a selected direction by hydraulic motor 12" to line the new track. The track lining mechanism is mounted at the forward end of the first car 13 of the rear train of the machine, over which the new ties are transported to the track laying station and which continuously receives the old track rails 6 as they are lifted off the ballast during the continuous forward movement of the entire machine in the manner fully described and illustrated in the aboveidentified patent and patent applications.

The reference system illustrated in FIG. 1 operates as follows.

In view of the fixed mounting of the laser beam emitter 7 on car 1, the laser beam reference 3 is at least approximately parallel to the elongation of the newly laid track 2. The laser beam receiver 10 runs with its rollers 11, 1 1 on the new rails 2, 2 and tends to follow the laser beam. For this purpose, the receiver has light and/or heat sensitive cells or elements mounted laterally on both sides of the center of the receiver. As soon as the laser beam fails to becentered on the receiver, a lateral deviation will be registered by the impingement of the beam on one of the light and/or heat sensitive cells to produce a control signal which is transmitted by circuit 10' to the control 12. The control 12 correspondingly operates the hydraulic motor 12" to move the track lining mechanism 12 laterally into one or the other direction until the new track is lined in respect of the old track so that the laser beam is again centered on the receiver. In this manner, the newly laid track rail remains aligned with the old track.

In principle, the track renewal machine of FIG. 2 is the same as that of FIG. 1 and, to avoid redundancy in the description, like structures operating in a like manner have been designated with the same reference numerals.

In this modification, the reference is constituted by a conical light or infra-red beam 16 and the position of the reference line 3' of this beam is again dependent solely on the position of the old track 6 in the uncorrected track section. This is accomplished in the following manner.

A rearmost car 1' is spaced along the old track behind car 1, the car 1' also being supported on the track by a pair of spaced running gears 4, 5. A light beam emitter 7' is fixedly mounted on car 1 and a masking means 17, such as a spotboard, is fixedly mounted on car 1' in the path of the beam 16 to determine the direction or position of the reference line 3' which is parallel to the old track. The lower portion of the beam is masked by the spotboard 17 so that only reference line 3' is received by receiver 10', the position of this reference line being dependent solely on the position of the old track. As shown, it ispreferred to center the beam emitter and the beam mask between the running gears of the respective cars 1 and 1.

The illustrated machine includes conventional transport mechanisms for removing old ties l4 and laying new ties 15 on the ballast. At the track correction position between the old train, represented by cars 1, 1, and the new train, there is arranged a ballast leveling machine 18 which determines the level of the new track consisting of new ties 15 and new rails 2. Thus, the ballast leveling machine constitutes, in fact, a track position correction tool for the new track.

The ballast leveling means consists of an endless ballast moving conveyor 19 extending transversely across the right of way in contact with the ballast to level the same. A hydraulic motor 18' is arranged to move the conveyor 19 vertically to a desired level of the ballast. The hydraulic motor is operated by control 19" in re sponse to a control signal produced by receiver 10' when the reference line 3' impinges on light and/or heat sensitive elements mounted vertically on both sides of the center of the receiver in a conventional manner. In this manner, the reference line 3', whose position depends solely on the position of the old truck, controls the level of the new track. If lateral alignment is also desired, lateral alignment means controlled in the manner of FIG. 1 or 3 may be used with the modification of FIG. 2.

In the modification of FIG. 3, wherein like structures operating in a like manner have again been designated by the same reference numerals as in the preceding figures to avoid redundancy in the description, a reference line for controlling track alignment is constituted by a tensioned wire 3". One end of the tensioned wire is anchored to a bracket extending laterally from car 1 and another end of the wire is anchored to a bracket extending laterally from a carriage running with flanged rollers 11 on new track 2. An intermediate station which, in conjunction with the forward end 20' of the wire determines its position, is constituted by a forked holder 17 mounted on a laterally extending bracket on car 1 in the path of the wire. This forked holder determines the vertical and lateral position of the'ten'sioned wire 3". The desired position of the reference wire is attained when the wire passes contactfree between the contacts of the holder 17. When the wire touches either one of the laterally positioned contacts wherebetween it passes, an electrical control signal is transmitted via relay 17" through electrical circuit 10" to control 12' which, in the same manner as in the embodiment of FIG. 1, operates the hydraulic jack 12" of the lining mechanism 12 to move the new track 2 in either lateral direction, dependent on the control signal from contact fork 17 until the control signal disappears as the wire looses contact with the fork.

As best shown in FIG. 4, the tensioned reference wire 3" may be used not only for lining the new track but also to level the same in respect of the level of the old track, with the aid of the ballast level lining machine 18, as described in connection with the embodiment of FIG. 2. As shown in FIG. 4, the vertically movable ballast leveling conveyor 19 carries a laterally extending bracket 21, which moves up and down with the conveyor. The bracket 21 carries at its outer end a wire sensor in the path of tensioned wire 3" and cooperating therewith, this sensor including a rotary potentiometer 23 and a pivotal contact fork 24 operating the potentiometer upon pivoting of the fork by the wire, the pivoting direction of the contact fork or holder 24 being indicated by a double-headed arrow. To control or take into account the superelevation of the track in track curves, the bracket 21 carries a conventional pendulum device 22 which indicates the superelevation of the track at this point.

As the freely pivotal fork or wire holder 24 is moved up or down by the wire 3" during the continuous advance of the machine and upon a change in the level of the old track, the vertical wire position being dependent only on this level, due to its positioning at end point 20 and intermediate station 17' in the uncorrected track section, the rotary poteniometer operated by the wire holder will transmit a control signal through electrical circuit 25 to operate the hydraulic motor 18 and correspondingly adjust the vertical position of ballast leveling conveyor 19. Thus, the vertical position of the ballast leveler and thus the level of the new track will always depend on the vertical position of the reference wire 3" which is determined solely by the level of the old track.

FIG. 4 also shows the guide rails for old rails 6 and new rails 2 which are mounted on brackets 26 laterally extending from the ballast leveling machine 18.

FIG. 5 illustrates a useful laser beam emitter producing a planar laser beam 3, the emitter being movable in all directions, as indicated by the double-headed arrows.

While the invention has been described and illustrated in connection with certain now preferred embodiments, many modifications and variations may occur to those skilled in the art without departing from the spirit and scope thereof.

We claim:

1. An apparatus for controlling the correction of the position of a newly laid track by a mobile track laying machine replacing the track in an old track section, said track laying machine including a track correction station and being arranged to move in a working direction from a newly laid corrected track section to a newly laid uncorrected track section, comprising a reference system including a reference associated with one of the track rails, said reference extending in a direction opposite to the working direction towards the track correction station between two end points spaced from each other. along the track one in the old track section and the other in the newly laid uncorrected track section, and means for positioning the reference solely in dependence on the position of the track in the old track section.

2. The apparatus of claim 1, wherein the reference is a reference line.

3. The apparatus of claim 2, wherein the reference line is a beam of infra-red radiation.

4. The apparatus of claim 2, wherein the reference line is a light beam. 7

5. The apparatus of claim 2, wherein the reference line is a laser beam.

6. The apparatus of claim 2, wherein the reference line is a tensioned wire.

7. The apparatus of claim 1, wherein the reference is a reference plane.

8. The apparatus of claim 7, wherein the reference plane is a laser beam.

9. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in a vertical direction.

10. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in a lateral direction.

11. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in dependence on two track points spaced from each other along the track in the old track section. I 12. The apparatus of claim 1, wherein the reference is a reference plane, and the reference positioning means is arranged to position the reference plane in dependence on two track points spaced from each other along the track in the old track section, the reference plane being fixed at one of the track points in respect of a plane perpendicular to the track plane.

13. The apparatus of claim 1, wherein reference is a reference plane, and the reference positioning means is arranged to position the reference plane in dependence on the two track points spaced from each other along the track in the old track section, the reference plane being fixed at one of the track points in respect of a plane parallel to the track plane.

14. The apparatus of claim 1, wherein the reference positioning means includes a frame guided along the associated track rail on two running gears spaced from each other along the track in the old track section.

15. The apparatus of claim 1, wherein the reference positioning means includes a control for positioning an end of the reference in the newly laid uncorrected track section, an intermediate station being arranged in the old track section for contact with the reference, and the control being operable in dependence on the position of the intermediate station.

16. The apparatus of claim 15, wherein the reference is a beam of electromagnetic radiation, further comprising a beam masking means at the intermediate station, the beam masking means being supported on the associated track rail, the distance of the beam masking means from the track rail corresponding to the distance of the reference end from the track.

17. The apparatus of claim 16, wherein the beam masking means is adjustably supported on the track rail for changing the distance therebetween.

18. The apparatus of claim 16, further comprising two frames at the intermediate station, the frames being spaced along the track and each frame being supported on the track by two running gears spaced from each other along the track, one of the frames being spaced farther from the track correction station carrying an emitter for the beam centrally between the running gears thereof, and the other frame being spaced closer to the track correction station carrying the beam masking means centrally between the running gears thereof.

19. The apparatus of claim 1, wherein the reference is a laser beam, and the reference positioning means includes a laser beam emitter constituting a forward end of the reference and solely determining the position of the laser beam, the laser beam emitter being adjustable in dependence on the position of the associated track rail in the old track section.

20. The apparatus of claim 19, further comprising a beam masking means in the path of the laser beam, the emitter being adjustable in response to the impingement of the-beam on the masking means.

21. The apparatus of claim 20, wherein the beam masking means includes light or heat sensitive elements responsive to impingement of the beam forcontrolling the adjustment of the emitter.

22. The apparatus of claim'19, further comprising a frame guided along the associated track rail on two running gears spaced from each other along the track in the uncorrected track section, the laser beam being fixedly mounted on the frame.

23. The apparatus ofclaim 1, wherein the reference is a tensioned wire, further comprising a mechanical element mounted at an intermediate station in the old track section for contact with the wire, and means for moving an end of the wire at the track correction statiori in response to a track correction movement to maintain the wire out of contact with the element.

24. The apparatus of claim 23, further comprising two frames spaced along the track in the old track section and each frame being supported on the track by two running gears spaced from each other along the track, each frame mounting a wire supporting element centrally between the running gearsthereof for determining the position of the wire.

25. The apparatus of claim 1, further comprising track working tools at the track correction station, and means for determining the difference between the actual and the desired position of the track at the track correction station.

26. The apparatus of claim 25, wherein the track working machine is a track lining and leveling machine, and the means for determining the difference between the actual and the desired track position includes a means for determining the difference between the actual and the desired lateral track position at an end of the reference at'the track correction station, and another means for determining the difference between the actual and the desired vertical track position between said end and the reference positioning means but closer to the reference end.

27. The apparatus of claim 26, wherein the track working tools, the end of the reference and the means for determining the difference between the actual and desired track position are mounted together at a forward end of the track lining and leveling machine, seen in the working direction.

28. The apparatus of claim 25, wherein the track working machine is mounted on two running gears spaced along the track, and the track working tools and an end of the reference are mounted together on the machine between the running gears thereof.

29. The apparatus of claim 28, wherein the track working machine is a track laying machine, and said working tools comprise ballast transport means and rail gripping means.

30. The apparatus of claim 25, wherein the track lay ing machine comprises two trains arranged to remove an old track and lay a new track, respectively, the working tools comprising means for leveling the ballast at the track correction station between said trains, and an end of the reference being mounted together with the working tools.

31. The apparatus of claim 29, wherein the reference positioning means is mounted on the forward train, seen in the direction of the working direction, and the track working tools are mounted on a forward end of the rear train, seen in said direction.

32. The apparatus of claim 1, further comprising means for adjusting the position of a forward end of the reference in the old track section.

33. The apparatus of claim 1, further comprising an intermediate station arranged in the old track section for contact with the reference to determine its position, and means for adjusting the position of the intermediate station to adjust the position of the reference. 

1. An apparatus for controlling the correction of the position of a newly laid track by a mobile track laying machine replacing the track in an old track section, said track laying machine including a track correction station and being arranged to move in a working direction from a newly laid corrected track section to a newly laid uncorrected track section, comprising a reference system including a reference associated with one of the track rails, said reference extending in a direction opposite to the working direction towards the track correction station between two end points spaced from each other along the track one in the old track section and the other in the newly laid uncorrected track section, and means for positioning the reference solely in dependence on the position of the track in the old track section.
 2. The apparatus of claim 1, wherein the reference is a reference line.
 3. The apparatus of claim 2, wherein the reference line is a beam of infra-red radiation.
 4. The apparatus of claim 2, wherein the reference line is a light beam.
 5. The apparatus of claim 2, wherein the reference line is a laser beam.
 6. The apparatus of claim 2, wherein the reference line is a tensioned wire.
 7. The apparatus of claim 1, wherein the reference is a reference plane.
 8. The apparatus of claim 7, wherein the reference plane is a laser beam.
 9. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in a vertical direction.
 10. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in a lateral direction.
 11. The apparatus of claim 1, wherein the reference positioning means is arranged to position the reference in dependence on two track points spaced from each other along the track in the old track section.
 12. The apparatus of claim 1, wherein the reference is a reference plane, and the reference positioning means is arranged to position the reference plane in dependence on two track points spaced from each other along the track in the old track section, the reference plane being fixed at one of the track points in respect of a plane perpendicular to the track plane.
 13. The apparatus of claim 1, wherein reference is a reference plane, and the reference positioning means is arranged to position the reference plane in dependence on the two track points spaced from each other along the track in the old track section, the reference plane being fixed at one of the track points in respect of a plane parallel to the track plane.
 14. The apparatus of claim 1, wherein the reference positioning means includes a frame guided along the associated track rail on two running gears spaced from each other along the track in the old track section.
 15. The apparatus of claim 1, wherein the reference positioning means includes a control for positioning an end of the reference in the newly laid uncorrected track section, an intermediate station being arranged in the old track section for contact with the reference, and the control being operable in dependence on the position of the intermediate station.
 16. The apparatus of claim 15, wherein the reference is a beam of electromagnetic radiation, further comprising a beam masking means at the intermediate station, the beam masking means being supported on the associated track rail, the distance of the beam masking means from the track rail corresponding to the distance of the reference end from the track.
 17. The apparatus of claim 16, wherein the beam masking means is adjustably supported on the track rail for changing the distance therebetween.
 18. The apparatus of claim 16, further comprising two frames at the intermediate station, the frames being spaced along the track and each frame being supported on the track by two running gears spaced from each other along the track, one of the frames being spaced farther from the track correction station carrying an emitter for the beam centrally between the running gears thereof, and the other frame being spaced closer to the track correction station carrying the beam masking means centrally between the running gears thereof.
 19. The apparatus of claim 1, wherein the reference is a laser beam, and the reference positioning means includes a laser beam emitter constituting a forward end of the reference and solely determining the position of the laser beam, the laser beam emitter being adjustable in dependence on the position of tHe associated track rail in the old track section.
 20. The apparatus of claim 19, further comprising a beam masking means in the path of the laser beam, the emitter being adjustable in response to the impingement of the beam on the masking means.
 21. The apparatus of claim 20, wherein the beam masking means includes light or heat sensitive elements responsive to impingement of the beam for controlling the adjustment of the emitter.
 22. The apparatus of claim 19, further comprising a frame guided along the associated track rail on two running gears spaced from each other along the track in the uncorrected track section, the laser beam being fixedly mounted on the frame.
 23. The apparatus of claim 1, wherein the reference is a tensioned wire, further comprising a mechanical element mounted at an intermediate station in the old track section for contact with the wire, and means for moving an end of the wire at the track correction station in response to a track correction movement to maintain the wire out of contact with the element.
 24. The apparatus of claim 23, further comprising two frames spaced along the track in the old track section and each frame being supported on the track by two running gears spaced from each other along the track, each frame mounting a wire supporting element centrally between the running gears thereof for determining the position of the wire.
 25. The apparatus of claim 1, further comprising track working tools at the track correction station, and means for determining the difference between the actual and the desired position of the track at the track correction station.
 26. The apparatus of claim 25, wherein the track working machine is a track lining and leveling machine, and the means for determining the difference between the actual and the desired track position includes a means for determining the difference between the actual and the desired lateral track position at an end of the reference at the track correction station, and another means for determining the difference between the actual and the desired vertical track position between said end and the reference positioning means but closer to the reference end.
 27. The apparatus of claim 26, wherein the track working tools, the end of the reference and the means for determining the difference between the actual and desired track position are mounted together at a forward end of the track lining and leveling machine, seen in the working direction.
 28. The apparatus of claim 25, wherein the track working machine is mounted on two running gears spaced along the track, and the track working tools and an end of the reference are mounted together on the machine between the running gears thereof.
 29. The apparatus of claim 28, wherein the track working machine is a track laying machine, and said working tools comprise ballast transport means and rail gripping means.
 30. The apparatus of claim 25, wherein the track laying machine comprises two trains arranged to remove an old track and lay a new track, respectively, the working tools comprising means for leveling the ballast at the track correction station between said trains, and an end of the reference being mounted together with the working tools.
 31. The apparatus of claim 29, wherein the reference positioning means is mounted on the forward train, seen in the direction of the working direction, and the track working tools are mounted on a forward end of the rear train, seen in said direction.
 32. The apparatus of claim 1, further comprising means for adjusting the position of a forward end of the reference in the old track section.
 33. The apparatus of claim 1, further comprising an intermediate station arranged in the old track section for contact with the reference to determine its position, and means for adjusting the position of the intermediate station to adjust the position of the reference. 